Impedance bridge, rebalancing, telemetric system



IMPEDANCE BRIDGE, REBALANCING, TELEMETRIC SYSTEM Filed July 18, 1946 April 11, 1950 J. F. GAUMER ETAL 2 Sheets-Sheet l A vv mmq April 11, 1950 IMPEDANCE BRiDGE, REBALANCING, TELEMETRIC SYSTEM Filed July 18, 1946 J. F. GAUMER ETAL 2,503,868

2 Sheets-Sheet 2 Patented Apr. 11, 1950 IMPEDANCE BRIDGE, REBALANCING, TELEMETRIC SYSTEM John F. Gaumer and Foster M. Poole, Dallas, Tex.; said Gaumer assignor to said Poole Application July 18, 1946, Serial No. 684,609

1 Claim. 1

This invention relates to control circuits, and with regard to certain more specific features, to a control circuit for telemetric systems utilizing a rebalancing impedance bridge.

This invention is an improvement upon the circuit shown in Fig. 21 of a copending United states patent application of Foster M. Poole (one of the inventors herein), Serial No. 649,650, dated February 23, 1946.

Among the several objects of the invention may be noted the provision of an improved bridge amplifier circuit for controllin the rotation of a two-phase, reversible control motor; the provision of means of the class described for reducing hunting of said motor; the provision of a circuit of the class described which will permit the use of substantial differences in transmitter and receiver coil sizes in the bridge circuit; and the provision of anti-hunting apparatus of the class described which is substantially instantaneously operable and which is simple in form. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claim.

In the accompanying drawings, in which several of various possible embodiments of the invention are illustrated,

Fig. 1 is a wiring diagram of one form of the invention; and,

Fig. 2 is a wiring diagram, corresponding to a part of Fig. 1 but showing a modification.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Where feasible in the drawings, reference characters have been used which correspond to those used in said Fig. 21 of said patent application.

In said patent application are shown certain dial drums or indicators I33 which are rotary with shaft 135 for the purpose of giving certain indications of measurements in response to the actions of exploring transmitters R (see said Fig. 21 in said application).

Each dial (also illustrated herein) is driven by a gear I31 attached to a shaft I35. Gear I3! is driven through a gear train I39 leading from a two-phase balancing motor MI. The motor MI is reversible and is connected into a circuit which is developed herein. Numeral I43 indicates an A. C. supply line. This supply line I43 supplies an impedance bridge circuit through an isolating transformer I45 and leads Ill. The isolating transformer may be omitted in some designs. The circuit consists of a coil I58 made up of a pair of coil sections 59 and a coil I5I composed of coil sections I52, all of which are interconnected through leads I48 and I50, and two armatures GI and I53. The armature BI is activated by a measurement transmitter R. Armature I53 is activated by a flexible band or linkage Ill, which is biased by spring I0 and is connected mechanically to the indicating dial drum I33. A switch 383 is used to deenergize the impedance bridge when desired.

The transmitter or detector R consists, among other elements, of feeler or detector balls 8| which, in being driven through a cylinder to be measured, move radially and transmit axial movement to a cone II. This axial movement is transmitted from the cone II to armature SI through a thrust bearing 69 and stem 51. This movement of armature GI through coil sections 59 will vary the electrical characteristics of the impedance bridge circuit, thus translating mechanical movement into electrical variations. Further details can be obtained by reference to my United States Patent 2,348,643.

The center tap I60 of each pair of coil sections 59 and I52 supplies an input transformer I55 via lines I49. This input transformer I55 feeds an amplifier network or circuit, indicated generally at I51, which through leads I59 feeds a control phase of the two phase reversible motor I ll The other and fixed phase of the motor is fed via leads I6I from the A. C. line I43.

Connected with the gear I31 on the shaft I35 is a pinion I63 which is meshed with a sector gear I65 swinging on a pivot I61. This sector gear I65 carries an arcuate shoe I69 over which is wrapped and connected the flexible band Ill such as a flexible steel ribbon. This ribbon is connected with the armature I53.

As described in said application. the motor Ill controls the position of its associated dial drum I33. When the feeler balls 8| are held in a predetermined position for proper diameter, the armature I53 may be considered to be in a position to hold its respective dial drum I33 at zero reference position for nominal diameter. For any deviations from a nominal diameter, the feeler balls 8| will change their radial positions, thus affecting movement of the cone II so as to reposition the armature 6|. This unbalances the impedance bridge circuit so as to energize the input side of the transformer I55. Any small unbalance is amplified in the amplifier I51 and applied by leads I59 to one phase of the motor Ill, the other phase of the motor being energized over connections I8I. Thus the motor I is caused to reposition the armature I53 to reestablish a new balance of the impedance bridge circuit. A low A. C. voltage arising from any minute unbalancing of the bridge is amplified sufiiciently to energize the balancing motor Ill. The phase of this A. C. voltage is dependent upon the direction of the movement of the armature 6 I The balancing motor Ill is of the reversible variable-speed induction type, one winding of which is continuously energized by line Voltage, the other energized by the amplified alternating voltage the phase of which, with respect to the line voltage, determines the direction of rotation of the motor. Thus the phase is in eifect recognized by the balancing motor I, hence determining its direction of rotation. As is known, any two-phase motor remains stationary when one of its phases is deenergized. Therefore, whenever there is no energization of the connection I59, the motor Ill will be stationary. The result is that the motor action follows the measuring action of the balls 8I, in one direction for plus deviation from a nominal diameter and in the reverse direction for minus deviation from said nominal diameter. tion and balancing of the impedance bridge circuit the dial drum I33 takes up a new position proportionately following the deviations from nominal diameter.

The above has been described in said application. The present invention has as its point of departure the provision of means for minimizing the hunting characteristics of such a motor as MI in making its adjustments.

Referring now more particularly to Fig. 1, any movement of armature M, as previously described, will cause a current to flow through the primary of transformer I55. The amount of this current flow will depend on the distance armature BI moves. The voltage developed across the primary of transformer I55 is therefore variable in amplitude and is also variable in phase, leading or lagging the line voltage, depending upon the direction of movement of the armature GI.

A voltage is induced in the secondary of transformer I55 and is proportionate to the primary voltage described above. This secondary voltage is impressed on a grid I of a vacuum tube 3. The amplifier reproduction of this grid voltage is developed across a plate load resistor 5, coupled through a condenser 1 to a grid 9 of a vacuum tube II. Vacuum tube II amplifies the signals impressed upon grid 9 and this amplified signal developed across a load resistor 2I, is coupled through condenser I3 to a grid I5 of a vacuum tube I9, the input signal to grid I5 being variable in amplitude by means of a potentiometer I1. The output signal of tube I9 is developed across a load resistor 23 and coupled to grids 21, 29, 3| and 33 of vacuum tubes I19, I8I, I83 and I85, respectively, through condenser 25.

Resistors 35, 31 are grid resistors, and condensers 31, 4| and 43 are used for both filtering and decoupling. Resistors l5 and 41 are used as decoupling resistors, and condenser 88 serves to by-pass unwanted spurious frequencies and harmonics. The power source for the described amplifier stages is the rectified output of a secondary winding 5| of a transformer 49, as rectifled by a vacuum tube 53. Condenser 51 and After each following acresistor 96 are conventionally connected to provide cathode bias for tube 3.

Tubes I19, I8I, I83 and I are connected in a push-push phase detecting circuit that also provides power amplification of the input signal impressed on grids 21, 29, 3I and 33. The anodes of tubes I19 and I85 are commonly connected to one end of a secondary winding I81, and the anodes of tubes I8I and I83 are commonly connected to the other end of secondary winding I81 of transformer 49, this transformer through two wires I59 supplying the power to the control phase I89 of the two-phase motor I M.

The output of alternating current to the control phase I89 of motor I will be controlled as to phase and amplitude by the signal impressed on grids 21, 29, 3| and 33. The bias for the power amplifier tubes I19, I8I, I83 and I85 is supplied from a tapped cathode bias resistor I9I, the lower section of which is normally shunted except when a limit switch I93 is opened.

It can be seen that any out-of-phase signal transmitted to the controlled phase I89 will cause the motor Ill to rotate, moving in turn armature I53 toward a position that will balance the impedance bridge, and it can also be seen that there is some tendency for armature I53,to be moved past a position necessary to balance the bridge. This overshooting oi the balance point will cause a signal to be impressed on controlled phase I89 that will be 188 out of phase with the original signal on controlled phase I89 and will therefore cause motor MI and armature I53 to move in the reverse direction. This action, or hunting, can be greatly decreased, by the addition of a feed-back circuit connected from the ungrounded end of controlled phase I89 through a wire I95, a condenser I91 and a resistor I99 to grid 9 of tube II. The signal sent through wire I95, condenser I91 and resistor I 99 will be in phase and proportional to the signal impressed on the controlled phase I89, but this signal will be 188 out of phase with the instantaneous signal impressed on grid 9 of tube II and will thereby tend to cancel it. The activating signal for controlled phase I89 will therefore be partially cancelled while still at a low level of amplification, such as at grid 9, and greatly decrease hunting.

The fixed-phase winding 28I of the two-phase motor is fed through two lines I6I from a conventional alternating current source, the latter also supplying power to the inductance bridge circuit, directly or through a transformer I45. Condensers 283 and 285 are phase shifting condensers of the type normally used with two-phase motors.

The transformer 49 is powered from an alternating current source, protected from overload by fuse 289, and it has a tapped primary 2 controlled by a switch 281, this switch being used in one position for higher than normal line voltages and in the other position for lower than normal line voltages. A secondary 2I3 of transformer 49 is used to supply power to the filament of the amplifier tube.

Although tubes I, II, I9, 53, I19, I8I, I85 and I83 are described as separate triode tubes, it is to be understood that duo-triode type tube: may be used. For example, tubes I19 and I8I could be paired in the same glass envelope of a single duo-triode tube and likewise tubes 3 and II; I9 and 53; I93 and I85.

In a bridge circuit of the type described above, ordinarily the two pairs of coil sections 59 and I52 were of substantially the same size. If, however, the size of the armature SI and coil sections 59 must be made very small, as would be necessary for the measurement of a very small diameter cylinder, certain difllculties would arise. Temperatures would occur in the small coil sections which would be higher than those in the then relatively larger coil sections I52. This is because the small coil sections would be carrying the same current as the larger coil sections. While balanced conditions could be brought about under different temperature conditions in coil sections 59 and I52, operators would, before measurements could be taken, need to wait until equilibrium temperature of the smaller modified coil sections 59 wasreached. This is a disadvantage. Furthermore, the design and construction under unequal temperature conditions would be diflicult. A system that will permit the use of a very small transmitting armature GI without reducing the size of armature I53 and coil sections I52 and without loss of accuracy or unequal temperature rises is shown in Fig. 2.

Referring now to Fig. 2, there is noted a small transmitter or detector 40I, consisting among other things of feeler balls 403 which, in being driven through a small cylinder to be measured, move radially and transmit axial movement to a cone 405. This axial movement is transmitted from the cone 405 to movable transmitter armature 407 through a thrust bearing 409 and a stem or linkage 4| I. The movement of this armature 401 will cause a variation in the current flow in coil sections 4I3, center-taps 421 and 429, wires 4", H9 and 42I, and this current variation in turn will affect the current flow through winding 423 of a transformer 5. This will result in variations in the electrical characteristics of a winding 425 which will cause an unbalance in the impedance bridge circuit including the end sections 424 of winding 425, coil sections I52 of winding II, wires 43I and I49. This in turn causes a signal to be impressed on transformer I55 through wires I49. The transformerwindings 424 are such, in view of the electrical chardo not appreciably heat them any more than coil sections I52 are heated. It can therefore be seen that a small movement in the armature 407, causing a small current variation in winding 423, will bring about a relatively great movement in balancing armature I59 to balance the electrical variation across winding 425 of transformer 5. This will give greatly increased accuracy of measurement and without undue heating of coils H3.

The use of the term impedance bridge circuit is intended to cover such a circuit wherein suitable resistances and capacitances are used with, or in place of the coils 59, 4 I 3 and I5 I.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope 6 of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim: Indicating apparatus comprising a detector, an

1 indicator, a two-phase reversible motor connected with said indicator to drive it back and forth, said motor having a fixed phase and a control phase, an impedance bridge circuit adapted to be thrown out of electrical balance by a movable transmitter armature and to be balanced by a movable balancing armature, said circuit including four coil inductances and a transformer, the impedance of a first two of said coil inductances being controlled by said transmitter armature, the impedance of asecond two of said coil inductances being controlled by said balancing armature, said second two inductances being physically larger in their coil forms than said first two inductances,the transformer having its primary connected to said first two inductances and its secondary connected to said latter two larger inductances, a first linkage for transmitting movement from said indicator to said balancing armature, a second linkage for transmitting movement from the detector to the transmitter armature, an amplifying network including at least two vacuum tube sections connected in a push-push circuit adapted variably to energize said control phase of the motor in response to an unbalanced condition in said impedance bridge circuit, and a feed-back circuit between the control phase of said motor and said amplifying network, the potential of said circuit being in phase with the potential of the control phase of the motor and approximately out of phase with the potential of said amplifying network at the point of connection thereto, the impedance of said first two inductances being substantially different than the impedance of said second two inductances when said armatures are in a balanced condition.

JOHN F. GAUMER. FOSTER M. POOLE.

REFERENCES CITED The following references are of record in the file of this patent:

, UNITED STATES PATENTS Number Name Date 1,708,910 Spencer Apr. 9, 1929 2,021,752 Suits Nov. 19, 1935 2,075,083 Bernarde Mar. 30, 1937 2,154,375 Chambers Apr. 11,1939 2,209,369 Wills July 30, 1940 2,234,349 Mackay Mar. 11, 1941 2,328,320 Baruch Aug. 31, 1943 2,406,221 Hornfeck Aug. 20, 1946 2,414,317 Middel Jan. 14, 1947 OTHER REFERENCES Radio Amateur's Handbook, 1941 edition, pages 34-56.

Publication: Telemetering and Totalizing, Borden; Instruments. December 1935, page 328. 

